1. Field of the Invention
This invention relates generally to toilets and is concerned primarily (but not exclusively) with toilets of the type known as "two-piece portable toilets".
Typically, a two-piece portable toilet comprises a bowl unit detachably secured to and supported by a holding tank. The bowl unit includes a bowl having a discharge outlet which communicates with an inlet at the top of the holding tank. The bowl unit incorporates a flush liquid reservoir formed around the bowl and a manually operable pump for discharging flush liquid into the bowl. The holding tank is provided with a valve mechanism which normally closes the holding tank inlet but which can be opened to allow waste to enter the holding tank from the bowl.
Each time the toilet is used, liquid passes from the flush liquid reservoir into the holding tank and the level of liquid in the reservoir falls while the level in the holding tank rises. The bowl unit is provided with a liquid inlet through which the reservoir can be periodically refilled and the holding tank is designed to be detached from the bowl unit so that it can be periodically emptied.
Determination of the times at which the reservoir should be refilled and the holding tank emptied has generally been left to visual observation by the user, of the flushing action of the toilet. When an attempt is made to flush the toilet but flush liquid does not appear, then the reservoir is refilled. In the case of the holding tank, visual observation through the discharge outlet of the bowl when the holding tank valve is open is used to determine the point at which the holding tank should be emptied.
2. Description of the Prior Art
Proposals have been made to provide the holding tank with a visual indicator for signaling when the holding tank is full. For example, U.S. Pat. No. 3,727,242 (Miller) shows an example of a liquid level indication apparatus in a recirculation-type toilet. This type of toilet has a holding tank from which liquid is recirculated through the bowl of the toilet and back into the tank. In the patented structure, a vertical slot is provided in the wall of the tank extending from the level of the inlet of a recirculation pump to the level of the bowl outlet, and a clear plastic prism is mounted in the slot and allows the liquid level to be monitored by viewing through the prism. While this form of indicator has the advantage of an absence of moving parts, it would have a serious aesthetic drawback in that the contents of the holding tank would be visible through the prism. Also, the indicator would be relatively expensive to manufacture both in terms of the cost of the components and the difficulty of forming a slot in the wall of the holding tank and sealing the prism in liquid-tight fashion in the slot.
Another form of liquid level indicator which has been used in the waste holding tank of a two-piece portable toilet involves a float which responds to the liquid level in the holding tank and which is used to turn an indicator drum located in an opening in the wall of the tank. The float is enclosed in a plastic bag which is sealed to the wall of the holding tank around the opening in which the drum is located. As the level of liquid within the holding tank rises, the float also rises inside its plastic bag until a maximum level is reached; the drum is marked to then indicate that the holding tank should be emptied.
This form of indicator suffers from a number of disadvantages, most of which stem from the fact that moving parts are involved. The float is prone to jam, for example due to the presence of tissue in the holding tank and/or to the presence of the plastic bag surrounding the float. Also, this form of indicator is quite costly to manufacture, again not only because of the cost of the components of the indicator, but also because of the difficulty of effectively sealing the float assembly against leakage.